The general goal of this study is to establish the link between visual cortical plasticity during the postnatal critical period and the central monoaminergic system. As an extension of our previous studies on this topic, we will explore, in particular, a way of modifying cortical plasticity by direct manipulation of monoaminergic receptor function. For this purpose, various receptor antagonists and agonists will be delivered continuously into the visual cortex (area 17) through a chronically implanted microperfusion system. Receptive field properties, binocularity in particular, of single visual cortical cells will be examined following eye occulsion in kittens and adult cats (single unit physiology). These animals will be concurrently subjected to a variety of manipulations of the central monoamine terminals and their receptors. The morphological correlates of changes in the ocular dominance distribution (width of ocuular dominance column) also will be studied in monocularly deprived and monoamine depleted animals (autoradiography).